1. Field of the Invention
The present invention relates to a method and a device for stabilizing a vehicle in extreme driving situations, e.g., when understeering while cornering.
2. Description of Related Art
Driving dynamics control systems such as ESP or DSC, for example, are used to improve the controllability of motor vehicles in critical driving situations, e.g. when oversteering or understeering in cornering, and to stabilize the vehicle. Known systems include a sensor system, which records measured values about the current driving condition of the vehicle, a control unit having a control algorithm for performing a sideslip angle and/or yaw rate control, and at least one actuator for influencing the driving behavior of the vehicle. Various setpoint variables are calculated from the driver input, in particular the steering wheel position and the accelerator pedal position and brake pedal position, and are compared to the actual variables. If the system deviation exceeds a specified threshold, then the driving dynamics control intervenes in the driving operation and produces a compensating yaw moment, which counteracts the yaw movement of the vehicle and straightens out the vehicle according to the setpoint specifications. For this purpose, known driving dynamics control systems usually use the vehicle brakes and/or the engine control as actuators or act on the steering via a steering actuator.
Driving dynamics controllers used today are usually designed in such a way that they brake the inside rear wheel if the vehicle is understeering. This produces a yaw moment in the direction of the inside of the curve, which makes the vehicle attack the curve with more intensity. The vehicle is thus able to follow tighter curve radii. At high driving speeds and correspondingly high transversal accelerations, however, there arises the problem that the inside wheels are greatly relieved of load and are thus only able to take up modest longitudinal forces. As a result it is no longer possible to perform an effective brake intervention on the inside rear wheel.
To improve vehicle stabilization, therefore, an additional controller function (known by acronym EUC) was introduced, which triggers an automatic braking action with the aim of decelerating the vehicle as a whole and to reduce the transverse forces (transversal acceleration). Within the scope of the function, the brake pressure on the wheel brakes of all four wheels is increased equally and the vehicle is decelerated. Braking the wheels, however, initially results in a decrease of the cornering stability potential. Hence there is initially an increased slip at the front wheels and thus an increased understeering of the vehicle. Only when the driving speed has sufficiently decreased is the vehicle again able to follow the steering angle.